Method of and apparatus for ascertaining the density of a stream of fibrous material

Abstract

The density of a trimmed stream of tobacco particles on a radiation-permeable conveyor is ascertained by directing a first beam of infrared light against the trimmed stream so that the light must pass through the stream and through the conveyor prior to reaching a detector which transmits to an evaluating circuit signals denoting the density of the trimmed stream. Such signals are corrected, when necessary, by signals which are generated by a second detector serving to monitor the intensity of infrared light which has passed only through the conveyor, and the corrected signals are used to regulate the operation of a trimming device which converts an untrimmed stream into the trimmed stream. Signals from the second detector indicate the extent of permeability changes of the conveyor as a result of accumulation of solid and/or liquid substances in or on the conveyor, and such signals can further serve to warn the operators that the conveyor is damaged and/or to modify the intensity of light which is caused to pass through the stream and through the conveyor and/or to modify the intensity of light which passes only through the conveyor.

We claim: 
     
       1. A method of ascertaining the density of a stream of fibrous material, such as a stream of tobacco particles, comprising the steps of transporting the stream along a predetermined path which is defined by a radiation-permeable conveyor; directing against the stream on the conveyor at least one beam of radiation so that the radiation penetrates through the stream and through the conveyor and the intensity of radiation which has penetrated through the stream and through the conveyor is indicative of density of the stream; monitoring the intensity of radiation which has penetrated through the stream and through the conveyor; generating a density signal denoting the monitored density; directing a second beam of radiation only through the conveyor so that the intensity of radiation of the second beam which penetrates through the conveyor is indicative of permeability of the conveyor to such radiation; monitoring the intensity of radiation which has penetrated only through the conveyor; generating a second signal denoting the monitored intensity of radiation which has penetrated only through the conveyor; and modifying the density signal in dependency upon the second signal to eliminate the influence of variations, if any, of permeability of the conveyor upon the density signal. 
     
     
       2. The method of claim 1, further comprising the steps of establishing and maintaining a source of radiation and dividing the radiation issuing from said source into said at least one beam and into said second beam. 
     
     
       3. The method of claim 1, wherein said modifying step includes varying the intensity of radiation in dependency upon changes, if any, of intensity of the second signal to compensate for variations of permeability of the conveyor. 
     
     
       4. The method of claim 1, further comprising the step of converting the second signal into a third signal denoting the condition of the conveyor. 
     
     
       5. The method of claim 1, wherein said modifying step includes varying the intensity of radiation in dependency upon changes, if any, of the second signal so as to maintain the intensity of the second signal at least close to a substantially constant value. 
     
     
       6. The method of claim 1, wherein said at least one beam contains optical radiation, particularly infrared light. 
     
     
       7. The method of claim 1, wherein each of said beams is a beam of optical radiation. 
     
     
       8. The method of claim 7, wherein each of said beams contains infrared light. 
     
     
       9. Apparatus for ascertaining the density of a stream of fibrous material, such as a stream of tobacco particles, comprising a radiation-permeable conveyor arranged to convey the stream along a predetermined path, said conveyor comprising a portion which is located outside of said path; density measuring means including a radiation source arranged to direct at least one beam of radiation through the stream in said path and through said conveyor whereby the intensity of radiation which has penetrated through the stream and through the conveyor is indicative of density of the stream, and means for monitoring the intensity of radiation which has penetrated through the stream and through the conveyor, including means for generating a signal denoting the monitored intensity of radiation; means for processing said signal into a density signal denoting the density of the stream in said path; second measuring means including a second radiation source arranged to direct at least one second beam of radiation only through said portion of said conveyor so that the intensity of radiation penetrating through said portion is indicative of permeability of the conveyor, and means for monitoring the intensity of radiation that penetrates through said portion of the conveyor, including means for generating a second signal denoting the monitored intensity of such radiation; and means for modifying said density signal in dependency upon said second signal to eliminate the influence of changes, if any, of permeability of said conveyor upon the density signal. 
     
     
       10. The apparatus of claim 9, wherein said processing means comprises means for converting the second signal into a signal denoting the permeability of said conveyor. 
     
     
       11. The apparatus of claim 9, wherein at least one of said sources emits optical radiation, particularly infrared light. 
     
     
       12. The apparatus of claim 9, wherein said processing means comprises means for converting the second signal into a third signal denoting the permeability of said conveyor. 
     
     
       13. The apparatus of claim 9, wherein said processing means includes means for converting the second signal into a third signal denoting the permeability of said conveyor, said modifying means comprising means for influencing the intensity of radiation issuing from at least one of said radiation sources in dependency upon said third signal to compensate for influence of changes, if any, of permeability of the conveyor upon the density signal. 
     
     
       14. The apparatus of claim 9, wherein said processing means includes means for converting said second signal into a third signal denoting the permeability of the conveyor and further comprising means for displaying said third signal. 
     
     
       15. The apparatus of claim 9, wherein said source emits optical radiation, particularly infrared light. 
     
     
       16. The apparatus of claim 9, further comprising a common radiation source and means for directing radiation from said common source to the sources of said measuring means. 
     
     
       17. The apparatus of claim 16, wherein said radiation directing means comprises optical fibers.